Increasingly over the past half century, air quality has become an issue of public concern. Over this period, the scientific community has steadily improved its understanding of the origins of the air pollution that is apparent over most major U.S. cities. A large part of this air pollution is attributable to the release of volatile organic compounds into the atmosphere. As a result, the reduction of the releases of volatile organic compounds has become an increasingly important part of the overall strategy to improve air quality.
The most familiar volatile compound reduction technique is the control of fuel vaporization by vapor recovery techniques, first on automobiles and now on gasoline stations located in nonobtainment areas. As a result, the steady year over year increase in U.S. releases of these compounds has leveled off and is now even declining.
Manufacturing sites are responsible for approximately 8.5 million tons of volatile organic compound emissions annually. Solvent vaporization or in some cases, hydrocarbon byproducts, are key to the manufacturing process of many of the items used regularly in daily life. The manufacture of familiar consumer products results in the release into the atmosphere of significant amounts of organic compounds such as pentane, ethanol, methanol, ethyl acetate, and many others. The control of volatile organic compounds is essential to the environmentally friendly manufacture of these products, and thus, there remains a struggle with the cost of control versus the loss of competitiveness.
The most common control method in use today is the thermal oxidizer. In connection with this method, the volatile solvent is released in amounts generally less than a few thousand parts per million into the plant air system. This air is then selectively collected and fed into a combustion chamber where it is mixed with enough natural gas to sustain combustion. It is then ignited in a large chamber that incinerates the volatile solvent, as well as, the natural gas, thereby producing carbon dioxide and water vapor as the primary products of combustion. These oxidizers are large, complicated devices that represent a major capital expense and require significant amounts of electricity and gas to operate. While heat can sometimes be recovered, generally speaking, thermal oxidizers represent a significant economic loss to the businesses using them. In a typical U.S. industrial plant, the cost of operating this type of device easily adds 25%, and often much more, to the yearly energy bill.
Another current control technology uses solvent recovery methods that pass the air from the plant through an activated charcoal filter. Periodically, the charcoal is heated, driving off highly concentrated volatile compounds into a chilled condensing system. The output is a liquid organic compound often requiring hazardous waste treatment. The cost of operation, as well as the initial capital costs, are significantly higher than the thermal oxidizer, thereby making this control technology less attractive for the majority of industrial sites.
Accordingly, an efficient and cost effective device for the destruction of volatile organic compounds is needed.
Such a device is described and claimed in the copending application U.S. Ser. No. 08/538,692, now U.S. Pat. No. 5,592,811, filed on Oct. 3, 1995, and owned by the assignee of record. The subject matter of that application is hereby incorporated herein by reference.
In that application, a system for the destruction of volatile organic compounds is disclosed which comprises a combustor and a reaction chamber, both of which are suitably connected to the compressor, such as the compressor of a power generator (e.g. a gas turbine engine). The system further comprises a primary inlet to the combustor for supplying a primary fuel and a secondary inlet to the combustor and the reaction chamber for supplying a secondary fuel. The secondary fuel comprises air and an amount of a volatile organic compound. The compressor compresses the secondary fuel and directs the compressed fuel to the combustor and reaction chamber. The fuel mixture is reacted in the reaction chamber, and the stream of combustion gases directed to a power generator to generate power.
While the system so described is suitable for use in many applications, once assembled, particularly if the combustor is provided for direct, in line communication with the inlet of the reaction chamber, the size of the device becomes cumbersome for shipping and maintenance.
Moreover, in operation of the device, particularly when the VOC laden air is drawn from environments which vary over time, i.e. the amount of VOCs in the air varies, control of the system can become difficult.